According to established orthodontic techniques, it is well known that one is able to ligate an archwire to a bracket utilizing an elastic or metal ligature. In a twin edgewise bracket, the elastic ligature is stretched around respective undercuts of gingival and occlusal tie wings so as to overlay the archwire at mesial and distal ends of the bracket.
The ligating procedure involves carefully stretching the elastic ligature (or wrapping and twisting a metal ligature) around the tie wings utilizing appropriate orthodontic instruments. It has been found that the time consuming ligation procedure contributes to lengthy chair time. Furthermore, the elastic ligatures are known to lose their elasticity with time and are subject to degradation. Also, the elastic and metal ligatures have been known to trap food particles in areas of the bracket which are difficult for the patient to clean, and to increase the level of friction against the archwire. Finally, the use of sharp metal ligatures around the bracket can subject the clinician to unnecessary exposure to infectious bacteria, or viruses such as hepatitis B, or possibly the HIV virus in blood.
In an effort to overcome these disadvantages of elastic ligatures, certain advances have been made in the area of self-engaging brackets. Each of U.S. Pat. Nos. 4,144,642; 4,248,588; 4,698,017; 3,772,787; 4,786,252; 4,559,012; 4,561,844; 4,655,708; 4,077,126; 4,419,078; 4,634,662; 4,197,642 and 4,712,999 illustrate one or more designs for self-engaging brackets.
Furthermore, my own U.S. patent application Ser. No. 08/007,095 filed on Jan. 21, 1993, and entitled Self-Engaging Orthodontic Bracket, describes an improved self-engaging twin orthodontic bracket having a generally U-shaped locking shutter which is slidably received in the base member of the bracket. These prior art devices overcome some of the disadvantages associated with elastic ligatures. Self-engaging brackets eliminate, or at least reduce exposure of the clinician to sharp ligatures, thereby alleviating the problem of contracting dangerous viruses. In addition, self-engaging brackets permit differential archwire contact separately for round and rectangular archwires at two different levels of contact, which is not possible with elastic or metal ligatures which interact with all individual archwires in a similar manner. However, most of the known prior art self-engaging brackets lack the reliability and ease of operability that most clinicians require.